The present invention relates to a method of producing a coated substrate with an adhesive composition. This invention requires a contact adhesive which is a polyurethane/urea composition consisting essentially of a) a polyisocyanate with a functionality of less than about 4, optionally, b) a polyol blend consisting of 1) about 95 to 100% polyether polyols with molecular weights from about 1800 to 12000 and average functionality from about 1.5 to about 4, and 2) up to about 5% of chain extenders with molecular weights from about 60 to 400 and average functionality from about 1.5 to about 3, and c) polyethers having at least two isocyanate reactive groups and a molecular weight of from about 1800 to about 12000 in which at least 50% of the isocyanate reactive groups are primary and/or secondary amino groups. The weight ratio of components b) to component c) ranges from about 95:5 to about 0:100, and the amounts of components a), b), and c) are such that the equivalent ratio of isocyanate groups to isocyanate-reactive groups is from about 85:100 to about 115:100 and the sum of the urethane group content plus the urea group content is from about 1 to about 12%. Substrates suitable for use in the present invention are preferably porous, flexible substrates. Coated substrates produced by this method are also the subject of the present invention.
Polyurethane adhesives and sealants of various types are well known. See, for example, U.S. Pat. Nos. 3,779,794, 4,156,064, 4,624,996, and 4,625,012.
In certain applications, it is desirable to provide an elastomeric material that can be applied to a flexible substrate in the liquid state and cured to provide an adhesive layer. This allows this flexible substrate to be attached to and in some cases subsequently removed from another surface.
Materials of this type are described in, for example, U.S. Pat. Nos. 5,102,714 and 5,227,409. These patents relate to adhesives for adhering carpet onto flooring based on a) a polyol mixture having an average functionality of 2.2 or less and equivalent weight of at least 500 and containing from 10 to 70 mole percent of monoalcohol and optionally up to 10% of a chain extender with an equivalent weight of from about 30 to 500, with b) a polyisocyanate mixture having an average functionality of about 2.2 or less.
Adhesives of this type are not useful for certain flexible substrates that are porous, such as, for example, textiles and other woven or nonwoven natural or synthetic fibers, paper and paper products, leather, or wood. When applying the adhesive materials in the liquid state onto these porous substrates, the reacting adhesives have a tendency to soak into the interior of the substrate before the adhesive can be cured. Because most of the applied adhesive is thus not on the surface of the substrate, the effectiveness of the cured adhesive is severely limited.
Adhesives containing high molecular weight amine terminated polyethers (ATPEs) are known. U.S. Pat. Nos. 4,743,672, 4,994,540 and U.S. Pat. No. 5,204,439 describe reactive polyurethane/urea adhesive compositions that do not sag when applied onto vertical surfaces. Like most polymeric materials containing urea linkages, these materials are somewhat brittle. These structural adhesives have a relatively high urethane plus urea content and are too brittle for use as contact adhesives for flexible, porous substrates.
U.S. Pat. No. 3,979,364 relates to caulking and sealants that do not sag when applied to vertical surfaces. Materials of this type are typically have a high content of mineral fillers, and are not useful as contact adhesives. The use of low molecular weight (i.e. 400-1500) amine terminated polyethers gives the desirable increase in viscosity upon combining the reactive components, but leads to solid gel particles that are undesirable in contact adhesives.
The polyurethane/urea contact adhesives of the present invention have several advantages. They can be applied to the substrates in liquid form and cured to form a permanently tacky elastomeric layer useful as a contact adhesive. The viscosity of the reacting adhesives is sufficiently high so that the compositions do not soak into porous substrates and thus remain on the surface of the substrate where they maintain their effectiveness as adhesive layers. The adhesives have sufficient flexibility so that they are useful on flexible substrates. Another advantage of the present invention is that the contact adhesives can be attached to and removed from a substrate, and are reusable.